This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. David Asner/LLNL 4 th ECFA/DESY Workshop April 1-4, 2003, NIKHEP, Amsterdam Resolved Photon Backgrounds to  Processes

Photons have Structure Three types of  collisions –Direct –Once resolved –Twice resolved Electroweak (DIS) Strong (  collider) “  ”=0.99  +.01 

Recent History Since SNOWMASS 2001 we have predicted backgrounds due to resolved photons to be “too large” – Telnov At St.Malo – de Roeck, Moenig, Schulte, Telnov – predict resolved photon background approximately an order of magnitude smaller At Prague – Asner & de Roeck discovered 1.Order of magnitude  Factor of 6 2.Not at all obvious why this large discrepancy exists Recently resolved this problem!

Procedure Set Pythia parameters Calculate cross sections Generate Luminosity distributions - CAIN Use above to generate stdhep output file Overlay these events in  physics studies

Resolved Photon Backgrounds:#1 Concern  collisions are NOT like e + e - 1.5x10 10 Primary e -,1x10 10 Compton  CAIN also includes e + e - from pair production and real  from beamstrahlung PYTHIA gamma/e- option simulates virtual  associated with e- beam Approximately 83% of interactions are  Approximately 17% of interactions are e  Approximately 0.4% of interactions are ee

Luminosity: CAIN

 Cross Section: Pythia vs Model

Cross Section: Pythia ,e ,ee Clearly e  cross section is NOT negligible, nor is luminosity  Must include in future studies

Scenarios 1)Default Pythia parameters: Most similar to the study by de Roeck, Schulte, Telnov 2)Preliminary Butterworth parameters: Used in our earlier work. 6x larger background. 3)Updated Butterworth parameters: –PARP(67)=4.0 vs 1.0 PARP(91)=1.0 vs 0.0 –PARP(81)=1.8 vs 1.5 PARP(99)=1.0 vs 0.0 –MSTP(82)= 1 vs 4  2 /dof = 4.96 vs 4.97 –Newer fit use ~ ¼ LEP, HERA, Tevatron luminosity 4)Repeat analysis for Higgs Factory, 500 GeV, type-I&II

# Overlay Events Recall  -NLC – rep. rate is 11.4kHz –1.5e10 10 e - /bunch –95 bunches/train –120 trains/second Higgs factory –6700 overlay events/second –56 events/train –0.6 events/crossing 500 GeV Machine ~3x larger

Occupancy: Tracks Cos  vs Energy (GeV) 3.7 tracks/crossing (|cos  | < 0.9) E avg = 0.7 GeV (p > 0.2 GeV) Plots correspond to bunch crossings

Occupancy: Showers Cos  vs Energy (GeV) 5.5 showers/crossing (|cos  | < 0.9) E avg = 0.4 GeV Plots correspond to bunch crossings

Impact on Higgs Reconstruction Higgs  bb Higgs  bb (no ) Higgs  bb (no + resolved bkgd)

Conclusions Agreement with de Roeck, Moenig, Schulte, Telnov Resolved photon backgrounds are weakly dependent on the choice of pythia settings e  backgrounds are not negligble ~ 20% effect 0.6 events/crossing at NLC Higgs Factory  1.2 at Tesla 3.7 tracks/crossing at 0.7 GeV 5.5 clusters/crossing at 0.4 GeV Challenges of resolved photon backgrounds appear to be smaller than those due to This background to be included in the next iteration of our Higgs analysis – accepted Phys. Rev. D.